In the manufacturing of automotive vehicles, it is customary to preassemble components of the chassis of the vehicle before marrying them with the vehicle body. The bringing together of the chassis and body takes place on a continuously moving conveyor line. The body is typically conveyed overhead by a conveyor, and the chassis components to be married to the body are supported by a fixture of a moving lift machine that operates to move the chassis components into position beneath the moving body while lifting the chassis components into position for assembly with the body.
Many of the lift machines in present use employ a pneumatically powered hydraulic lift mechanism to raise and lower the fixture or fixtures that carry the chassis components. Some machines have a single fixture, whereas others are equipped with two such fixtures provided at opposite ends of the lift machine. Each fixture has its own hydraulic system and the two are often synchronized to operate in unison.
The hydraulic systems each include a fluid cylinder that is mounted on the machine and secured to its associated fixture. A pair of multi-stage telescoping vertical guides are provided on opposite sides of each cylinder and guide the fixture vertically.
A longitudinally extending cabinet projects above a base of the machine in the space between the fixtures and houses various components associated with the control and operation of the hydraulic/pneumatic systems. Among the components accommodated within the cabinet is a reservoir containing hydraulic fluid to be supplied to the cylinders, and an onboard pneumatic pump system that drives the hydraulics. Then pump system has onboard rechargeable air tanks also housed in the cabinet that hold a supply of pressurized air for operating the pump. The pump in turn controls the flow of hydraulic fluid to and from the cylinders in order to raise and lower the platforms.
While the traditional hydraulic/pneumatic lift mechanism of such machines performs satisfactorily in raising and lowering the platforms, it has several inherent disadvantages which add cost and complexity to the operation, many of which are unique to the art of chassis component lift machines.
The hydraulic systems have various seals, fittings and other components that are prone to frequent leakage and failure and require the constant attention of skilled workmen to maintain them in working order. It also requires that a fairly large capacity hydraulic fluid reservoir be carried on board the machine to supply fluid to the cylinders, adding to the size, cost and weight of the machines.
The rechargeable pneumatic pump system presents its own set of problems. The pump relies for its power on the supply of pressurized air from the onboard tanks. When the air in the tanks is exhausted, the pump and thus the hydraulics are no longer operational. A spent machine must be routed out of the normal assembly loop to a specialized recharge station where the tanks are refilled with pressurized air. During this time, another machine must be introduced in its place to support the continuous assembly operation. Since a full charge typically provides at most three lift cycles before requiring recharging, a number of extra machines must be kept on hand to support the assembly operation, adding further to the cost of supporting the operation. The specially equipped charging stations also add to the cost of the operation and can occupy valuable floor space of a facility.
Another objection inherent with the existing hydraulic/pneumatic lift system is that the elevated cabinet needs to be fairly tall in order to house the various components of the hydraulic/pneumatic system. The presence of the elevated cabinet can obstruct full access to the components supported on the fixtures to those assisting in the assembly operation, and particularly their step-through passage across the machine, making it less convenient to reach certain areas.
A chassis lift apparatus constructed in accordance with the present invention overcomes or greatly minimizes the foregoing objections to conventional hydraulic/pneumatic chassis lift machines.